*{
    margin: 0;
    padding: 0;
}

html{
    font-size: 10px;
}

section{
    width: 100rem;
    margin:  5rem auto;
}
ul{
    height: 5rem;
    display: flex;
    flex-direction: row;
  
}

ul li {
    list-style-type: none;
    background-color: gray;
    flex-grow: 1;
    font-size: 3rem;
    text-align: center;

    cursor: pointer;
}
.active{
    background-color: red;
}